1. Field of the Invention
This invention relates to a PTC thermistor, particularly to one able to surely separate and insulate two electric conducting plates with different electrodes positioned inside the PTC thermistor, able to insure safety when the PTC thermistor makes electrical connection.
2. Description of the Prior Art
A conventional PTC thermistor disclosed in a U.S. Pat. No. 5,125,070, titled “PTC THERMISTOR” (Positive Temperature Coefficient Thermistor), which is devised by the inventor of this invention, as shown in FIGS. 1, 2 and 3, includes a plurality of beehive-shaped PTC thermal resistance members 10, two metal conducting plates 11, 12, two insulating plates 13 and two heat-conducting plates 15.
The beehive-shaped PTC thermal resistance members 10 are provided in the center of the PTC thermistor, and the two metal conducting plates 11, 12 are respectively positioned at the opposite sides of the PTC thermal resistance members 10, having their surfaces respectively bored with a plurality of openings 110, 120 at locations respectively aligned to each PTC thermal resistance member 10. Each opening 110 of the conducting plate 11 has its inner wall protruding out and forming wing strips separated and formed with positioning recesses 111 tallying with one side area of each PTC thermal resistance member 10, while each opening 120 of the conducting plate 12 has its inner wall formed integral with elastic strips 121 protruding toward the other side of the PTC thermal resistance member 10. The two insulating plates 13 with plural openings are respectively disposed at the outer side of the two conducting plates 11 and 12. After foresaid components of the conventional PTC thermistor are combined together, the power-connecting terminal 112 and 122 of the conducting plate 11, 12 are respectively connected with a power source to let the opposite sides of the PTC thermal resistance members 10 electrically connected and heated to produce a heat source, and then wind generated by a fan blows toward the PTC thermistor to exhaust out the heat of the PTC thermal resistance members 10 through the openings 110, 120 of the conducting plate 11, 12 and the openings of the two insulating plates 13. In addition, to avoid overheat of the two conducting plates 11, 12 due to contact with the two sides of the PTC thermal resistance members 10, the conventional PTC thermistor is additionally provided with two heat-conducting plates 15 respectively positioned between the conducting plates 11 and 12 and the insulating plate 13 to contact with the conducting plates 11 and 12 for dispersing high temperature of the two conducting plates 11, 12.
After the conventional PTC thermistor is assembled, as shown in FIGS. 2 and 3, the PTC thermal resistance members 10 are firmly clamped between the two electric conducting plates 11, 12, and the two heat-conducting plates 15 and the two insulating plates 13 are respectively and orderly disposed at the outer side of the conducting plate 11, 12, and then all the components are combined together by the locking members 14. Thus, each PTC thermal resistance member 10 has one side engaged in the positioning recesses 111 of the first conducting plate 11 and the other side held by the elastic strips 121 of the second conducting plate 12, letting the PTC thermal resistance members 10 closely clamped by the two conducting plates 11 and 12. The power-connecting terminals 112 and 122 of the electric conducting plates 11 and 12 are respectively connected with a positive electrode and a negative electrode, and when electrically connected, the opposite sides of the PTC thermal resistance members 10 will immediately be heated to form a heat source.
However, in the conventional PTC thermistor, the electric conducting plates 11 and 12 respectively connected with a positive and negative electrode are separated only by the PTC thermal resistance members that are formed with a little thickness and arranged separately; therefore, the two electric conducting plates 11 and 12 with different electrodes are spaced apart only with a small gap to lower their insulation effect. Moreover, if the locking members 14 employed for combining the components are respectively locked with uneven tightness to shorten the distance between the two electric conducting plates 11 and 12, the two conducting plates 11, 12 will lose insulation effect and most likely to contact with each other and cause short current, resulting in a danger. In addition, the PTC thermal resistance members 10 are clamped and fixed between the two conducting plates 11 and 12 by having one side a only a little inserted in the shallow positioning recesses 111 of the first conducting plate 11 and the other side supported by the elastic strips 121 of the second conducting plate 12. Thus, the PTC thermal resistance members 10 are easy to slip off because the positioning recesses 111 of the first conducting plate 11 are not deep enough to hold them tight.